High performance liquid chromatography (HPLC) and UPLC® liquid chromatography systems require a stable high pressure system flow over operational pressure ranges. By way of example, system pressures may be less than a few thousand pounds per square inch (psi) (14 megapascals (MPa)) to more than 20,000 psi (140 MPa), depending on the system capabilities and the specific application. In another example, an inject pressure used for a prime and purge cycle may be 150 psi (1.0 MPa). Pressure sensors can be used to obtain pressure measurements at multiple locations within the system for verification of proper pressure and to accurately maintain a specified system pressure.
Flow through pressure sensors are typically preferred over other types of pressure sensor for chromatography applications to minimize dead volume in the flow path. Dead volume can result in trapped sample or other fluid components and may lead to cross-contamination in subsequent chromatographic separations. Conventional flow through pressure sensors typically employ a strain gage and sensor circuitry that may include a wheatstone bridge and signal processing components. These flow through pressure sensors are limited in the range of pressure that can be measured. Using such pressure sensors over an increased pressure range can lead to premature failure and increasing amplification in the sensor circuitry can result in signal degradation. Moreover, these sensors can be difficult to manufacture, assemble and test.
Conventional flow through pressure sensors can be manufactured with different bore wall thicknesses between the plane of the strain gage surface to which the strain gage is attached and the wall of the bore that contains or passes the pressurized fluid. Each bore wall thickness corresponds to a limited range of pressures that can be accurately measured. As a result, a number of sensors of similar configuration but different bore wall thicknesses for the strain gage surface are required to cover a wide range of pressures.